1. Field of the Invention
This invention relates generally to semiconductor fabrication, and more particularly to a CMP system and a processing fluid dispensing system therefore.
2. Description of the Related Art
Conventional chemical mechanical planarization ("CMP") processes involve the planarization of a surface of a wafer or workpiece through the use of an abrasive slurry and various rinses and solvents. Material removal from the workpiece surface is through a combination of abrasive action and chemical reaction. In many processes, a quantity of abrasive slurry is introduced onto a polish pad of the CMP tool and distributed across the surface thereof by means of centrifugal force. Thereafter, one or more wafers are brought into sliding contact with the polish pad for a select period of time.
In many conventional CMP systems, processing fluids such as slurries, solvents and rinses are dispensed from a static dispense tube that is centrally positioned above the polish pad. The polish pad is fitted with an upwardly projecting dispersal cone that is designed to disperse processing fluid dispensed from above laterally across the polishing surface of the polish pad. The action of the fluid flowing down the sloped surfaces of the dispersal cone along with centrifugal force associated with the rotation of the polish pad is intended to provide a fairly uniform layer of processing fluid across the surface of the polish pad.
The planarity of a surface following CMP processing is dependent upon a variety of factors, such as the initial uniformity of the slurry prior to CMP, the uniformity of the slurry dispensed on a polish pad prior to wafer landing and during processing, and the uniformity in force applied to the wafer, among others. The initial uniformity of the slurry is dependent on quality control by the slurry manufacturer and upon proper handling prior to CMP processing. Uniform force application depends on the functioning of the wafer handling elements of the CMP tool, the condition of the polish pad and the density of the underlying slurry. Slurry uniformity after dispersal depends several factors. One significant factor is the method of fluid delivery employed by the CMP tool.
There are several disadvantages associated with conventional CMP tool fluid delivery systems. Reliance upon centrifugal force as the primary mechanism for dispersal of slurry across the polish pad surface can lead to slurry stagnation at the outer edge of the polish pad. Slurry stagnation near the outer edge of a polish pad is also a result of a combination of other mechanisms, such as the gradual dilution of the slurry due to the radially outward flow of waste products removed from the wafer surface during polishing, and the lack of an adequate real time refreshing of slurry onto the polish pad from the fluid dispensing system. Accordingly, in areas of the polish pad where slurry stagnation is occurring, there will be less reactants, and thus less than optimal polishing for those portions of wafer surfaces that are polished by that portion of the polish pad.
Time and slurry consumption are two other disadvantages associated with conventional CMP systems. For both oxide and metal CMP processes conducted on various conventional CMP tools, a polish pad pre-wet segment must be performed prior to wafer landing. The pre-wet segment may last about 30 seconds and consume about 500 ml of slurry/polish run. This cycle time and slurry consumption is a necessary though undesirable consequence of the use of a pump fed fluid delivery system in conjunction with the aforementioned dispersal cone and polish pad rotation to provide centrifugal force dispersal of the fluid across the polish pad.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.